Vulcanizing rubber



Patented Sept. 18, 1934 Fri 1,973,914 VULCANIZING RUBBER George H.Stevens, Newark, N. J.

No Drawing. Applicationv July 1, 1929, Serial No. 375,064

18 Claims. (c1.1s- 53) This invention relates to improvements in the useof organic nitrogenous substances that assist in or accelerate thevulcanization of rubber and similar materials, and has for its objectthe utilization of new chemical reactions and new substances to thisend. i

This application is a continuation in part of: Serial llumber 215,511filed Aug. 25, 1927, now Patent 1,551,987, that relates to the use ofthe mono-substituted guanidine derivatives of monoaryl substitutedcarbodiimide; Ser. No. 215,512 filed Aug. 1927, that relates to the useof the trisubstituted guanidine derivatives of diaryl substitutedcarbodiimide; and Ser. No. 258,148 filed Feb. 29, 1928, now Patent1,925,707 that relates to the use of monoand tritolyl substitutedguanidines, or their higher homologues, in combination.

In Ser. No. 651,968 filed July 16, 1923, now Patent 1,921,375 I haveclaimed the use of a combination of carbomonosubstituted imide andcarbodisubstituted imide, with ammonia and a homologue of aniline as anaccelerator. I have also broadly claimed therein the use of acceleratorsthat comprise monoand trisubstituted guanidines used in combination. Thehigher homoiogues of the former, in combination with the higherhomologues of the latter, and solid solutions comprising any of thesesubstances in such combination, form within certain limitations, thesubject matter of the present invention.

Guanidine, theaddition product of cyanamide ammonia, is an accelerator,and even with a substitution of its hydrogen it retains the samestructure, and is th same nucleus compound, so

within the different primary and secondary am which themselves are alsoaccelerators and from which the substituting groups are derived, restthe main diiierences in the nurnerous substituted guanidines thatresult, and which therefore must all be accelerators, but with physicalch mical properties that vary greatly.

Under a disassociation by heat, the disassociation products of theseguanidine compounds then progressively polymerise into more or lessquantity of melamine-s.

i-alonoaryl substituted guanidines are addition products of monoarylsubstituted carbodiimides (monoaryl substituted cyanamides),

ammonia. i aryl substituted guani'dinesof symmetrical fc myare additionproducts of diaryl substituted carbodiimides and primary amines of thebenzene series, such as aniline, toluidine, xylidine, cumidi-ne,duridine, or their methyl, ethyl, propyl, butyl, or higher homologousalkyl modifications, wherein the substituted carbodiimide and primarymonamine possess any of these single monovalent aromatic groups.

Triaryl substituted guanidines of unsymmetrical form, are additionproducts of diaryl substituted cyanamide and the aforementioned primaryaryl monamines, or are addition products of monoaryl substitutedcarbodiimides and secondary inonamines or" thebenzene series, such asdiphenylamine, ditolylamine, dixylilamine, dicumylamine, didurylaznine,or their mixed bases, phenyl-tolylamine, phenyl-xylilamine,phenyl-cumylamine, phenyl-durylamine, tolyl-Xylilamine,'tOIyLcumylamine, tolyl-durylamine, xylil-cumylamine, xylil-durylainine,cumyldurylamine, or the secondary phenyl-alkylamines, such asethyl-aniline, methyl aniline, propyl aniline, and butyl aniline, or anyother secondary amines that possess any of these double or bivalentaromatic or phenyl-alkyl, or alkyl-benzene substituting groups.

The trisubstituted 'guanidines contain then the substituting groups ofboth of their compo nents.

Diaryl substituted guanidines of symmetrical form, are addition productsof diaryl substituted carbodiimides and ammonia, or of monoarylsubstituted carbodiimides and the aforementioned primary amines.

Under disassociation by heat, which is not materially different invulcanization than outside of it, these substituted guanidines break upor disassociate into the same components again, the reactions beingusually reversible.

Under such disassociation, the monosubstituted guanidines split oft"ammonia, but the symmetrical and unsymmetrical trisubstituted guanidinessplit off an aryl amine instead.

The symmetrical and unsymmetrical disubstituted guanidines underdisassociation' however, split oiT both ammonia and an aryl amine.

In addition then-to the above amines split off by heat, the principaldisassociation product of monosubstituted guanidine is monosubstitutedcarbodiimide, while that of symmetrical trisubstituted guanidine isdisubstituted carbodiimide.

Symmetrical (ll-"substituted guanidine however, disassociates into bothmonoand (11- substituted carbodiimide, and unsymmetrical trisubstitutedguanidines disassociate into both monoand di-'"substituted"cyanamide.

Only symmetrical disubstituted and unsymmetrical'trisubstitutedguanidines then disas- 110 sociate into both monoand disubstitutedcarbodiimides or cyanamides respectively.

The foregoing mono-, di-, and tri-, substituted guanidines underdisassociation by heat, then gradually and progressively form arylsubstituted melamines, which are the trimolecular polymerizationproducts that result upon combining three molecules of any of theaforementioned aryl substituted carbodiimide-, or aryl substitutedcyanamidedisassociation products of these substituted guanidines, andthese melamines are all useful in vulcanization.

The main disassociation product of monosubstituted guanidine ismonosubstituted carbodiimide which polymerises to trisubstitutedisomelamine, while that of symmetrical trisubstituted guanidine isdisubstituted carbodiimide which polymerises to hexasubstitutedisomelamine, and that of unsymmetrical disubstituted guanidine andsymmetrical tetrasubstituted guanidine is a disubstituted cyanamide thatpolymerise's to persubstituted, or heXasubstituted normal melamine.These substituted melamines in each case indicating that but one form ofsubstituted carbodiimide, or substituted cyanamide, was present in thedisassociation.

The disassociation products of symmetrical disubstituted guanidinecomprising both monoand disubstituted carbodiimide, can polymerise 1 totetrasubstituted isomelamine, and those of uns mmetrical trisubstitutedguanidine comprising both monoand disubstituted cyanamide, canpolymerise to tetrasubstituted normal melamine.

Only symmetrical disubstituted, and unsymmetrical trisubstitutedguanidines then under disassociation, result in both monoanddisubstituted carbodiimides, or cyanamides, respectively, that canpolymeriseto tetrasubstituted melamines, and the former symmetricaldisubstituted guanidine is the only one of these that also has ammoniapresent in its disassociation.

Under the heat of vulcanization, substituted guanidine acceleratorsdisassociate, and simultaneously the catalytic function of acceleratingvulcanization is then carried out, through some cycle reaction thatinvolves these several'disassociation components, because molecularrelations between 100 parts of rubber and .05 part of accelerator wouldbe out of the question (Ostromislensky, The Action of the Amines andMetallic Oxides on vulcanization, Jour. 'Russ. Phys. Chem. Soc. 4'7,1915, 1892-1893).

So long as ammonia is present in the disassociation, under the action ofheat it will activate any of these imide or cyanamide bodies, or eventheir melamines, thereby causing them to continue to function asaccelerators, and so long as primary or secondary monamines are presentin the disassociation, under the action of heat. they will activate anyof the monomolecular forms of they substituted carbodiimides, though ina lesser manner, but as the carbodiimide or cyanamide bodiesprogressively polymerise to diand jtrimolecular forms, such activationby the monamines becomes lessened, until with the melamine it is at itsminimum, and when both the ammonia and monamine have become dissipatedthrough the heat of vulcanizatiom-such conversion to substitutedmelamineinhibits accordingly any further interreaction, or acceleration,as

tho melamines cannot easily supply ammonia or aryl aminesfor furthercycle reactions.

In using disubstituted guanidine accelerators i then, the diversityoftheir disassociation prodcelerators, the presence then of anytetrasubstituted melamine in the resultant vulcanized compound,indicates that both a monoand a disubstituted carbodiimide or cyanamidewere present in the vulcanization, and if the melamine is ofthe'isoform, that is a tetrasubstituted tricarbodiimide, that bothammonia and an aryl amine had also been present in the vulcanization,and therefore a suitable diversity of disassociation components had beenpresent for the requisite interreactions, or cycle reactions, whereas ifthe melamine is of the normal form, that an aryl amine was the onlyamine that was present in the vulcanization.

It is apparent therefore, that between different substituted guanidineaccelerators having similar substituting aromatic groups, that the onethat splits oif the most ammonia, and that ultimate- 1y can form themost tetrasubstituted melamine, will be the most practical accelerator.

After an accelerated vulcanization is completed, it is obwlous that theaccelerator then should become as inert as possible.

To inhibit such further vulcanizing activity, where the acceleratorstill retains some of its original characteristics, or where itscomponents are of low melting point, is usually difficult, but if theaccelerator be so structurally constituted as to permit of a slow changeduring vulcanization, to a different, high melting, lesser activecompound, then its catalytic function in such new form becomesrestricted, and just such a transformation is found to take place in thegradual formation of these high melting aryl substituted melamines, thatresult from the disassociatlon products of the several aryl substitutedguanidines described.

Where the nucleus of each carbodiimide molecule is of symmetrical form,the resultant melamine is an aryl substituted isomelamine, or

aryl substituted tricarbodiimide, but where the nucleus of eachcomponent molecule is of unsymmetrical form as in cyanamide, theresultant melamine is an arylsubstituted normal melamine.

Both symmetricaland unsymmetrical forms of theinonc molecular componentsmay be present in the same molecule of substituted melamine, or themelamine may even contain molecules of cyanamide.

The higher molecular weight aryl substituted melamines usually havequite high melting points, which thereby materially aids theirwithdrawal from acceleration after their complementary amines aredissipated.

It is apparent then, that where either a symmetrical mono or symmetricaltrisubstituted guanidine is used alone, no formation either oil thenormal or of the isoforms of a tetrasubstituted melanine could bepossible from these components, respectively. 7

While it is possible however, for an unsymmetrical trisubstitutedguanidine to disassociate into four components that may be capable of aforming tetrasubstituted m'elamines, no "ammonia however will be foundpresent in such disassociation, and the melamine will not be of theisoform.

But where either symmetrical or unsymmetrical diaryl substitutedguanidine is used, should any interreaction or cycle reaction takeplace, there will be four disassociation components present includingammonia, that are capable of interreactions to monoand trisubstitutedguanidines, as well as to the original symmetrical disubstitutedguanidine started with, or to guanidine and tetrasubstituted guanidines,as well as to the original unsymmetrical disubstituted guanidine startedwith, though the disassociation components of the symmetrical body only,are capable of forming a tetrasubstituted melamine. g a

That is, any guanidine accelerator, that under heat will break up intofour disassociation components that include ammonia, and the componentssuitably diversified so that a tetrasubstituted isomelamine can formtherefrom, oifers a greater opportunity for such interreactions or cyclereactions taking place, than is ofiered by a guanidine accelerator thathas no ammonia present in its disassociation, or where itsdisassociation components are limited to only reverse reactions, or arenot sufiiciently diversified to permit of a tetrasubstituted isomelaminebeing formed therefrom.

The chemistry of the foregoing guanidine substances being wellestablished, it isplainly evident then that a like diversity ofdisassociation components, and the same resultant tetrasubstitutedisomelamine, but in a greater amount of each, will be found through ause of monoand trisubstituted guanidines in conjunction with each other,for in such cases both ammonia and an aryl amine, and both a monoand adisubstituted carbodiimide or (11- substituted cyanamide will also bepresent in the acceleration, and a tetrasubstituted melamine can alsoresult therefrom, in just the same manner as occurs in using symmetricaldiaryl substituted guanidines,

Under their disassociation by heat, molecular proportions of monoandtriaryl substituted guanidines will release a much larger percent ofammonia, while from two molecular proportions of the former and one ofthe latter the accomsame guanidine, or whether the substituting aromaticgroups be the same, or are different in constitution in the two guandines, and any such combinations of monoand tri-substituted guanidinewill prove of superior value as accelerators in those cases whereammonia is possible of being split off in the disassociation, and thedisassociation products are capable of forming tetra aryl substitutedmelamines, whether the substituting groups in the melamine be alike, orare isomerically different, or are different in composition.

That is, a greater and more prolonged interreaction activity ispossible, through the use of monoand triaryl substituted guanidines incombination, than is possible where the mono-, di-, or trisimilarlysubstituted guanidines respectively are used alone.

Ammonia is a strong base, but its basic character is diminished orpartially neutralized however, when a phenyl radical substitutes one ofthe hydrogens in ammonia, as in primary phenyl amine, whereas thesubstitution of an alkyl group instead has the opposite effect, as inthe alkylamines which are even stronger bases than ammonia, and theirbasicity is duly increased as the number of alkyl substitutions thereinisincreased.

The phenyl radical then is of a somewhat negative character, but as itbecomes modified by methyl substitutions this negative character 1changes, the same as with the alkylamines, and its basicity therebyincreases, and this change becomes especially noticeable when two ormore such methyl or alkyl substituting groups have been introduced intothe phenyl radical or" an aryl amine.

Purely secondary aryl amines of the type of diphenyl amine are evenfeebler bases than the 100 corresponding primary aryl amines, but wheresuch secondary aryl amines are mixed bases, of the type of phenyl-tolylamine, or of the phenylalkylamines mentioned, then they havemarkedlybasis properties.

As these primary and secondary aryl amines may be considered asmonoaryl, or diaryl substituted ammonia, the difference in the basicityof the aryl amine rests then, mainly in the djferences in theirsubstituting groups.

This phenomenon of increased basicity, due both to mixed groups, and topolymethyl substitutions in the aromatic groups, continues in the arylsubstituted guanidines having substituting radicals derived from thesearyl amines, not 115 only where these mixed divalent groups take theplace of two amino hydrogens in guanidine, or where polymethyl groupstake the place of hydrogen in substituting aromatic groups, but alsowhere any use of mixed aryl substituted guanidine compounds involves twoor more aromatic groups that are diflerent in composition, andparticularly where aromatic groups are involved that contain a pluralityof alkyl substitutions.

The basicity of such-guanidine compounds increases therefore, not onlyfrom a mixing of the substituting aromatic groups, but increases mainlyaccording to the degree of modification of the phenyl radical by methylor alkyl substitutions, and such increased basic character in aguanidine compound is indicative of increased accelerating properties.

The accelerating substances particularly comprised by this applicationare then, those monoand trisubstituted guanidines used in combination,that are characterized by having substituting aromatic groups that havebeen derived from either primary or secondary amines of the hen zeneseries, wherein an aromatic group in at least one of the substitutedguanidines contains a plurality of methyl (CH3), substitutions. Suchmethyl groups may replace hydrogen in the ben-' zene ring, or replacehydrogen in other methyl groups that are either in the benzene ring, orare in theside chain of the aromatic group that substitutes the hydrogenin guanidine, Such. aro-- matic groups then'will contain more than?carbon atoms. l

Suitable monosubstituted guanidines that idine (1:2:41526).

Amidodimethyl benzene substituted guanidines having a singlesubstituting aromatic group, and of which the following are examples:

Mono ortho-Xylil guanidine (1:2:6). Mono- OlllllG-X'y'lll guanidine(1:2:4). Monometa-xylil guanidine (123:5). Monometa-xylil guanidine(1:3:6). Monometa-Xylil guanidine (1:312). Monopara-xylil guanidine(114:5).

Amidotrimethyl benzene substituted guanidines having a singlesubstituting aromatic group, and of which the following are examples:

Monocuroyl guanidine (1:23:40 Monocumyl guanidine (133:4:2)- Monoctunylguanidine (1:3:516) Monocumylz guanidine (1:2:3z5). Monocumyl guanidine(1:2:445) Including the groups from mesitylene, hemimellithene, and thepseudocumidines.

Amidotetramethyl benzene substituted guanidines having a singlesubstituting group and of which the following are examples;

Monoduryl guanidine (l:2:3:4:6) Monoduryl guanidine (1:3:4:5:6) Monoduryl guan Including the groups from prehnitene and isodurene.

The amidopentamethyl benzene mono! substituted guanidine (1:2:3:4:5:6),is also'an example.

Or any monosubstituted guanidine having a benzene ring substitution,with the benzene ring having either polymethyl substitutions, 'or hav-'ing methyl and other alkyl' substitutions, or. having alkylsubstitutions forhydrogen of the methyl substitutions, and furtherexamples of which will be found in the:

Monosubstituted guanidines with propyl or isopropyl-benzenesubstitutions,or with methylpropyl or methylisopropyl-benzenesubstitutions, or with polymethylpropyl' or polymethylisopropyl benzenesubstitutions, or any similar monoaryl substituted guanidines thatcontain ethyl, butyl, or homologous groups in either the normal or iso-.forms of the alkyl-benzene homologues, all of which are to be consideredas monosubstituted guanidines, the substituting groups of which containa plurality of methyl substitutions.

Suitable trisubstituted guanidines that may be used according to myinvention, are those having substituting groups similar to any of thosein group that contains a plurality-0f methyl sub:

stitutions.

The disassociation products of these monoand trisubstitutec guanidinesthat are utilized-in the aforementioned combinations, are those monoanddisubstituted carbodiimides and disub-. stituted cyanamides, havingsubstituting groups similar to any of those in the ortho-, para-, meta-,or other aforementioned isomeric forms of xylil, 'cumyl, duryl, orhomologous polymethyl benzene monosubstituted guanidines mentioned,together with primary 'or secondary amines of the benzene series havinga similar group, or groups homologous thereto, and ammonia.

Monocumyl guanidinev (1:'3:4:5

prising both guanidines can The tetrae substituted melamines, ortrimolecular polymerization products that may form from using monoandtrisubstituted guanidines in the aforementioned combinations, are thosehaving four substituting groups similar to any of those inthe ortho-,para-, meta-, or other aforementioned isomeric forms of xylil, cumyl,duryl, or homologous polymethyl benzene monosubstituted guanidinesmentioned, or similar to those in their substituted carbodiimides, orsubstituted cyanamides, whether the substituting groups are alike, orisomerically different, or different in composition in the samesubstituted melamine molecule, or whether the resultant tetra--substituted melamine forms as a mixture of differently substitutedmelamine molecules.

Examples showing the use of my invention are given in the followingvulcanizable compounds:

82 lbs, smoked sheets, 5 lbs. zinc oxide, 7 lbs. barytes, and 51/ lbs.sulphur, may constitute the compounded rubber; ,towhich addfii ozs.monoxylil substituted guanidine, and 5 ozs. trixylil substitutedguanidine. Heat the vulcanizable compound at 40 lbs. steam pressure for25 to 35 minutes to vulcanize.

Or, instead, 2 ozs. mono-, phenyl substituted guanidine and 5 ozs. tri-Xylil substituted guanidine;- or 2 ozs. monotolyl substituted guanidineand 5 ozs. tricumyl substituted guanidine; or 2 /2 ozs. monodurylsubstituted guanidine and 5 ozs. triduryl substituted guanidine; or 2%ozs. mono- 1netaxylil guanidine and 5 ozs. of trisubstituted guanidinehaving phenyl and paratolyl substituting groups; or 2 ozs; monocumylsubstituted guanidine and 5 ozs. trisubstituted guanidlne having tolyland Xylil substituting groups; may be added separately, as a mixture, oras a solid solution, to the above quantity of compounded rubber, andthen vulcanize.

As the substituted guanidines that are particularly comprised by myinvention possess aromatic groups that contain a plurality of methyl oralkyl substitutionathey are then the higher homologues orhighermolecular weight bodies of the series, frequently with highmelting points, and sotheyusually exist in numerous isomeric forms, andbecause these several isomers are dii ficult to separate from eachother, two or more such substituted guanidine isomerides may be usedtogether, and preferably in the form of a solid solution, that is, injust the mixed form that the combined or mixed substituted guanidinebase maybe precipitated from its neutralized acid salt solution inmanufacturing, and in consequence have a lowered or modified meltingpoint.

Material advantages are also frequently gained by using differentlysubstituted guanidines in combination, as for example where thesubstituting groupsv of the two guanidines different x in composition,and particularly where one of the substituted guanidines a melting pointmaterially higher thanthe temperature of vulcanization, and alone may bedeficient in activity as an accelerator. In such case a solid solutioncombe made, whereby the higher melting point is loweredand single orcommon melting point for both guanidines results, and the solid solutionaccelerator becom s thereby more effective for vulcanization purposes.

Such a solid solutionof monoand trisubstituted guanidines can be made byadding the acid salt solution of one guanidine to the acid salt solutionof the other guanidine and then neutral- -v 1 Hil i In icing andprecipitating together as a solid solution of both substitutedguanidines, which solid solution will be a substance that will have asingle or common melting point of all the constituent substitutedguanidines.- V

The interreactions that are shown as possible between the disassociationproducts of the various substituted guanidines mentioned, thereforefurnish adequate reasons for using, and my experiments confirm theadvantages to be gained, in the combined use of these mono and trisubstituted guanidines as accelerators. The incorporation into rubberthen-of a combination of monosubstituted guanidine and trisubstitutedguanidine, with at least one of the guanidines having substitutingaromatic groups that contain a plurality of methyl substitutions, andthe disassociation' products of which will comprise carbomonosubstitutedimide (monosubstituted cyanamide), carbodisubstituted imide (ordisubstituted cyanamide), ammonia, and aniline or homologue thereof, ora combination of any equivalent of these same substances as anaccelerator, broadly constitutes the present invention, or: anyacceleration of vulcanization that results from heating rubber with anequivalent combination of, desulphurised monoaryl substituted thioureaand desulphurised diaryl substituted thiourea, in the presence ofammonia, and aniline or homologue thereof, is to be considered ascomprised by this invention, and such broad invention was set forth inthe original specification and claims of Ser. No. 651,968 but in thepresent application has been limited to requiring that at least one ofthe substituting aromatic groups, in any such combination of monoandtrisubstituted guanidines, or in any such combination of theirequivalent components, must have a plurality of methyl substitutions.

Having now described my invention, and having shown the manner in whichthe products mentioned may be prepared and utilized, what I claim asnew, and desire to secure by Letters Patent is:

1. A process of vulcanizing rubber which consists in, incorporating intorubber an accelerator comprising the combination of a monoxylilguanidine and a trixylil guanidine, then heating the resultant rubbermixture with a vulcanizing agent to effect vulcanization. v

2. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that comprises thecombination of a monoxylil substituted guanidine and a mixture oftrixylil substituted guanidines, then heating the resultant rubbermixture with a vulcanizing agent to effect vulcanization.

3. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that comprises thecombination of a mixture of monoxylil substisubstituted guanidines, thenheating the resultant rubber mixture with a vulcanizing agent to eiiectvulcanization.

5. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar-materialan accelerator that comprises thecombination of a mixture of monoxylil substituted guanidines includingmonometa-xylil guanidine, and a mixture of trixylil substitutedguanidines including trimeta-xylil guanidine, then heating the resultantrubber mixture with a vulcanizing agent to effect vulcanization.

6; A process of vulcanizing rubber which consists; in, combining withcompounded rubber'or similar material an accelerator that comprises thecombination of a .monoxylil substituted guanidine,- and a trisubstituted'guanidine having substituting aromatic groups, wherein at leastone'or"- the aromatic groups of the combination contains apluralityof.methyl substitutions, then heating the resultant rubber mixture with avulcanizing agent to effect vulcanization.

Z. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that comprises thecombination of a monosubstituted guanidine having a substitutingaromatic group that contains a plurality of methyl substitutions, and atrixylil substituted guanidine, then heating the resultant rubbermixture with a vulcanizing agent to effect vulcanization.

8. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that comprises thecombination of a monosubstituted guanidine and a trisubstitutedguanidine, each of the guanidines having substituting aromatic groups,and at least one of the aromatic groups of the combination containing aplurality of methyl substitutions, then heating the resultant rubbermixture with a vulcanizing agent to effect vulcanization.

9. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that comprises thecombination of a mixture of monosubstituted guanidines and a mixture oftrisubstituted guanidines, each of the guanidines having substitutingaromatic groups, and at least one of the aromatic groups of thecombination containing a plurality of methyl substitutions, then heatingthe resultant rubber mixture with a vulcanizing agent to effectvulcanization.

10. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that comprises thecombination of a monosubstituted guanidine, having an aromatic group ofmore than 7 carbon atoms substituted on the alpha nitrogen atom withhydrogen atoms on the gammanitrogen atom, and a trisubstitutedguanidine, having an aromatic group of more than 7 carbon atomssubstituted on both the alphaand gammanitrogen atoms, and each of thearomatic groups containing a plurality of alkyl substitutions, thenheating the resultant rubber mixture with a vulcanizing agent to efiectvulcanization.

11. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that comprises thecombination of a monosubstituted guanidine, and a trisubstitutedguanidine having substituting aromatic groups, and wherein at least oneof the aromatic groups of the combination contains a plurality of methylsubstitutions, then heating the resultant rubber mixture with a vulcanizing agent to eifect vulcanization.

12. A process of vulcanizing rubber which consists in, combining withcompounded rubber or similar material an accelerator that compriseshaving a substituting aromatic group that contains a plurality of methylsubstitutions, and-a trisubstituted guanidine, then heatingthe-resultant rubber mixture with a vulcanizing agent to efifectvulcanization. 7

13. A process of vulcanizing rubber which con sistsin, combining withcompounded rubber-or similar material on accelerator that comprises thecombination of a solid solution of monosubstituted guanidine and a solidsolutionof tri-' substituted guanidine, each of the guanidines hav-' ingsubstituting aromatic groups, and with at least one of the aromaticgroups of the combination containing a plurality of methylsubstitutions, then heating the resultant rubber mixture with avulcanizing agent to efiect vulcanization.

14. That process of vulcanizing rubber characterized by heatingcompounded rubber or similar material with a vulcanizing agent togetherwith a solid solution of monoand tri: substituted guanidines, each ofthe guanidines having substituting aromatic groups, and with at leastone of the the combination of a mono! substituted-guanidine aromaticgroups of the combination containing a plurality of methylsubstitutions. r 15. A vulcanizable composition comprising rubher, avulcanizing agent, monoxylil substituted guanidine, and trixylilsubstituted guanidine.

- '16. A vulcanized rubber obtained by inducing a reaction betweenrubber, a vulcanizing agent,- a mono- Xylil substituted guanidine, and atrixylil substituted guanidine.

17. Vulcanized rubber products vulcanized with the addition of a smallamount or a mixture of mono- Xylil substituted guanidine and tri- Xylilsubstituted guanidinev 1 18. A vulcanized compound derived fromcompounded rubber or similar material, combined with a vulcanizing agentand an accelerator comprising a monosubstituted guanidine and atrisubstituted guanidine, with at least one of the guanidine's havingsubstituting aromatic groups, and with at least one of the aromaticgroups 01' the combination containing a plurality of methylsubstitutions.

GEORGE H. STEVENS.

